Observation of shell effects in superconducting nanoparticles of Sn

TL;DR

This study provides the first experimental evidence of shell effects causing giant oscillations in the superconducting energy gap of Sn nanoparticles, highlighting quantum size effects' role in nanoscale superconductivity.

Contribution

It demonstrates shell effects in superconducting nanoparticles and explains their dependence on coherence length, advancing understanding of quantum size effects in superconductivity.

Findings

Giant oscillations in Sn nanoparticle energy gaps observed

No oscillations detected in Pb nanoparticles due to coherence length differences

Quantum size effects can significantly enhance superconductivity in nanosystems

Abstract

In a zero-dimensional superconductor, quantum size effects(QSE) not only set the limit to superconductivity, but are also at the heart of new phenomena such as shell effects, which have been predicted to result in large enhancements of the superconducting energy gap. Here, we experimentally demonstrate these QSE through measurements on single, isolated Pb and Sn nanoparticles. In both systems superconductivity is ultimately quenched at sizes governed by the dominance of the quantum fluctuations of the order parameter. However, before the destruction of superconductivity, in Sn nanoparticles we observe giant oscillations in the superconducting energy gap with particle size leading to enhancements as large as 60%. These oscillations are the first experimental proof of coherent shell effects in nanoscale superconductors. Contrarily, we observe no such oscillations in the gap for Pb nanoparticles, which is ascribed to the suppression of shell effects for shorter coherence lengths. Our study paves the way to exploit QSE in boosting superconductivity in low-dimensional systems.